Large-scale generation of electric power based on solar irradiance continues progressing as an attractive modality for clean and efficient generation of electric power. Solar irradiance may reach a horizontal surface on the earth along two main paths, such as directly from the sun and by way of diffuse irradiance, which does not arrive on a direct path from the sun (e.g., has no defined direction) since it is made up of irradiance scattered by molecules and/or particles in the atmosphere. Depending upon cloud conditions and/or time of day (e.g., solar altitude), both the total amount of irradiance (e.g., global irradiance) and the respective proportions of direct and diffuse irradiance, which make up the global irradiance, may vary greatly.
Often a measurement of at least one or both of those solar irradiance components may be needed to, for example, estimate the power conversion efficiency of a solar-based power generation system at a given location. For example, measurements of direct irradiance may be of particular interest in concentrating solar thermal systems and/or in systems that track the position of the sun. By way of comparison, measurements of diffuse irradiance may be of more relevance in photovoltaic-based (PV-based) systems.
In the case of measurements of diffuse irradiance, it is known to use some kind of mechanically-rotatable shadowing device, where a shadowing mechanical structure, such as ball, ring or band, generally involves a costly and complicated mechanical contraption to meet a required mechanical tracking accuracy, which may be difficult to consistently realize over a long period of time in the outdoors. A further undesirable characteristic of such devices may be measurement errors introduced by the shadowing mechanical structure, which may physically block at least some of the field of view needed to accurately capture the diffuse irradiance component. In the case of measurements of direct irradiance, high-intensity irradiance may cause sensor burn-in effects which may shorten reliable operation of a sensor over time.
In view of the foregoing considerations, it would be desirable to provide an improved apparatus, such as may be able to reliably and at a relatively lower cost be able to accurately measure selected different components of solar irradiance.